1. Field of the Invention
This invention relates to an outer electrode for a spark plug and a method of manufacturing thereof which includes a center electrode placed within a metallic shell through an insulator with the outer electrode located to oppose to the center electrode through a spark gap, and particularly concerns to an outer electrode for a spark plug and a method of manufacturing thereof in which a rear end of the outer electrode is securely connected to a front end of the metallic shell by means of welding.
2. Description of the Prior Art
In an outer electrode for use in a spark plug which is usually employed to an internal combustion engine, the outer electrode has one end securely welded to a metallic shell which includes a center electrode placed within the metallic shell through an insulator with the outer electrode physically bent to oppose to the center electrode through a spark gap.
The outer electrode, thus welded to the metallic shell, has generally been made of nickel-based alloy by adding Si Cr, Al and Mn to 95% or more nickel which has a heat-dissipating (heat-conductive) property in addition to a heat and spark-erosion resistant property.
With a recent high-output engine, however, it has been desired to introduce an outer electrode especially superior in heat-dissipating (heat-conductive) property.
In order to cope with the recent desire, it is suggested that the outer electrode is made of a copper core which has a good heat-dissipating (heat-conductive) property. Due to relatively weak strength of a welding portion between the outer electrode and the metallic shell, cracks often occur on the welding portion when the outer electrode is physically bent to substantially form a L-shaped configuration.
With the welding portion carrying cracks, it is supposed that the core made of copper comes to lose its good heat-dissipating property so as to result in a limitted extension period of service life when mounted on an internal combustion engine.
Therefore, it is an object of the invention to provide an outer electrode for a spark plug which is capable of maintaining a good heat-dissipating property, and at the same time, obtaining a strong adhesion between an outer electrode and a metallic shell so as to insure an extended period of service life.